Field of the Invention
The present disclosure relates generally to electric vehicles. More particularly, the present disclosure relates to a road bearing that is adapted for high-power inductive power transfer between an electric vehicle and a power source embedded in a roadway.
Related Art
Recent environmental, economic and geopolitical concerns have spurred significant interest and development in electric vehicles, and many advances have been made in electric vehicles in recent years. However, factors such as battery weight, cost, charging time and energy capacity still present significant hurdles to the widespread adoption and use of electric vehicles in place of those powered by internal combustion engines. While battery costs are dropping and energy densities are increasing, the efficiency and affordability of these systems present continuing challenges. Given the current pace of battery development, it is estimated that widespread use of vehicles that employ batteries and other electrical storage devices is not likely to displace the internal combustion engine in the near future, unless heavily subsidized by governments. Even then, the subsidies required would be significant and may be required for a substantial time.
Advances in super-capacitors have been identified as one technology that could be used in place of electrical storage batteries. Indeed, some electric vehicles that are known today include one or more super-capacitors that are integrated with the electrical battery system. High capacity batteries take a long time to charge. Super-capacitors, on the other hand, charge hundreds of times faster. However, capacitor energy density (watt-hours per kilogram) is relatively small when compared to batteries, though it is improving. One researcher has reported production of a super-capacitor with an energy density similar to a lead-acid battery (about 35 watt-hours per kilogram). Another researcher has reported a super-capacitor with an energy density of 64 watt-hours per kilogram, and which can fully charge in 16 seconds and can recharge 10,000 times without significant degradation. In comparison, lithium-ion batteries holds about 200 watt-hours per kilogram. Super-capacitors by themselves do not appear ready to solve the charging time and weight challenges presented by electrical storage batteries for electric vehicles. It is believed that, as they emerge, Electric Vehicles (EVs) will be capable of accepting high power. The method for providing high power to EVs remains a question.
For many years, trolleys and busses have used systems that provide grid power to moving vehicles. Trolley buses and trains can have direct, electrical connection during operation, but it is not believed that private vehicles have been developed that exhibit this attribute. Moreover, electric trolleys and buses typically use continuous overhead catenary wire systems, which create complicated, overhead intersections, are visually distracting, are exposed to environmental hazards, and present significant construction and maintenance costs. These sorts of electrical distribution systems are generally considered impractical for private vehicles, and this and other factors tend to limit this sort of electric grid deployment.
Advantageously, various systems have been conceived for providing a connection between the electric grid and electric vehicles on a roadway without the use of continuous overhead wires. Business and academia around the world are analyzing not only the electrification of vehicles, but also the electrification of roads. One useful development that has been presented is the use of an air bearing for an electrical pickup device, as described in U.S. Pat. No. 8,556,050. This patent describes an electrical pickup device for an electric vehicle that creates an air bearing between the pickup device and an electrical supply line or coils embedded in the roadway. With this type of air bearing connection, air is supplied from the vehicle and cushions the power pickup coils as the electrical pickup device slides over the road. Air bearing induction can provide fast charging using lightweight vehicle coils because it can maintain a very small gap between the electrical supply coil in the road and the power pickup device. Induction without an air bearing tends to involve a relatively large gap between the road and the vehicle coils, which typically results in induction coils that are much heavier.
While air bearings can provide a useful connection between the electric grid and electric vehicles on a roadway, apparatus and methods for providing a suitable connection between the vehicle and the electric grid are needed. For example, an air bearing's air cushion can be very thin, which puts a premium on the flatness and smoothness of a road surface. When the smoothness requirement is met, an air bearing requires relatively little power and can be very quiet. Unfortunately, typical roads do not meet the smoothness requirement for satisfactory air bearing operation.
The present disclosure is directed toward one or more of the above issues.